Persistent, widespread pulsating aurora: A case study

Observations of a pulsating aurora event occurring on 11 February 2008, using the Time History of Events and Macroscale Interactions during Substorms (THEMIS) All-Sky Imager (ASI) array, indicate a spatially and temporally continuous event with a duration of greater than 15h and covering a region with a maximum size of greater than 10h magnetic local time. The optical pulsations are at times locally interrupted or drowned out by auroral substorm activity but are observed in the same location once the discrete aurora recedes. The pulsations following the auroral breakup appear to be brighter and have a larger patch size than before breakup. This suggests that, while the onset of pulsating aurora is not necessarily dependent upon a substorm precursor, the pulsations are affected and possibly enhanced by the substorm process. The long duration of this pulsating aurora event, lasting approximately 8h without interruption as imaged from Gillam station, is significantly longer than the typical 2-3h substorm recovery phase, suggesting that pulsating aurora is not strictly a recovery phase phenomenon. This paper is accompanied by a movie of the THEMIS ASI array data, from 0000 to 1715UT, plotted in mosaic and superimposed onto a map of North America.